This invention relates to a new and novel CRT device for generating a bright green light spot of the type that is particularly useful for projection color television and information display.
Green light radiation for use in projection color television generally is produced by the electronic bombardment of a green luminescent terbium activated phosphor such as a terbium activated yttrium oxysulfide phosphor. While the terbium activated phosphor when excited by electronic bombardment produces a high amount of the desired fundamental radiation at 544 nm, significant amounts of troublesome radiations at 490 nm, 586 nm and 620 nm are also produced. While the radiation at 586 nm is most troublesome as this radiation is the closest to the fundamental radiation and can cause blurring of the image when the 544 nm radiation is brought into focus, additional blurring can also be caused by the presence of the 490 nm and 620 nm radiations. In addition the presence of these radiations at 490 nm and 620 nm distorts the resultant image.
In order to significantly decrease the radiation at 586 nm, while causing essentially no reduction of the desired emission at 544 nm, the applicant, in his co-pending patent application Ser. No. 453,379, filed Dec. 27, 1982, teaches the use of a filtering composition comprising a solution of a soluble praseodymium salt. While the praseodymium salt containing filtering solution of this co-pending patent application significantly reduces the radiation at 586 nm while causing practically no decrease in the desired radiation at 544 nm it has only a very small effect on the undesired radiation at 490 nm, and no effect on the radiation at 620 nm.
British Patent application U.K. No. 2098393A to Sony Corporation discloses a green luminescent cathode ray tube containing a terbium activated yttrium oxysulfide phosphor and a filtering composition containing a mixture of brilliant blue and methyl orange for reducing the undesired radiations at the 490 nm, the 586 nm and the 620 nm lobes. While the filtering solution of the British patent does indeed substantially reduce these undesired radiations it also results in a very large undesired decrease in the desired radiation at 544 nm.